One-time programming (OTP) elements have been employed as memory elements, which are programmable only once.
OTP elements can be used for various purposes, including rescuing fail bits in a memory chip, writing chip identification data (ID) or an encryption code for preventing unauthorized use, or trimming an analog element after it is manufactured.
OTP elements include one type programmed by using the conductivity of a conductive film (the former type is referred to as fuse elements), and another type programmed by inducing or not inducing insulation breakdown in an insulator film (the latter type is referred to as anti-fuse elements).
Another technique has been also known in which a fuse is provide right above an anti-fuse, sandwiching an interlayer insulating film interposed therebetween, thereby reducing a space occupied thereby, together with coupling the anti-fuse and the fuse in parallel, such that the disconnected route can be reconnected once again, to enable reprogramming only once.